1. Field of the Invention
The present invention generally relates to information handling methods and systems based on a non-stop operating basis and, more particularly, to an information handling method and system which can increase the number of terminals that can be included in the system without stopping services to the terminals.
2. Description of the Related Art
As an on-line system is expanded, the number of terminals to be connected therein increases, and the processing load of a host computer increases. For the purpose of reducing the load to obtain a higher quality of service, there has been conventionally developed a distributed processing system which allows mutual usage of resources on a plurality of host computers through communication between the host computers.
In such a multi-computer system, in particular in an information handling system, terminals, computers for providing service to the terminals, and a host computer for collecting data from external devices outside the system have been connected in a vertical line to form a hierarchical structure. Communication between the elements in the same hierarchy has been carried out in a one-to-one correspondence relation through an element upward by one rank. An example of such prior art systems is shown in FIG. 2. The prior art system of FIG. 2 includes CPUs 01 and 11 to 1n, disc units 1 and 21 to 2n, terminal control units 41 to 4m, and terminals 511 to 5mk.
In order to enhance the reliability of such a system, conventionally, each pair of the system elements have been arranged on a multiplex or redundancy basis, and the elements have been handled in such pair-element units.
One such system is disclosed in, for example, literature entitled "Fault Tolerant System", written by Grey and translated by Eiichi Watanabe, MacGraw Hill K.K., 1986.
This prior art system, however, has had a problem in that communication between two elements in the system, in particular communication between two elements performing the same function, must be carried out through an upper-ranked element so that, when a fault occurs in the upper element or when the upper element is to be repaired or expanded, difficult communication between the lower elements results, thus disabling redundancy or take-over of the business. As related art, there are cited U.S. Pat. Nos. 4,366,479, 4,477,881 and 4,462,075 and a U.S. application Ser. No. 448,942 filed Dec. 12, 1989 entitled "Method and System For Information Distribution Services" (British Patent Application No. 8928106.5).